I have a 84 Vett with a 383, XRam and 2 inch TBs. The block is zero decked with a compression of 10.4:1. Full roller block, TFS heads, the cam is 218/224 @ 0.05 and the lift is .526/.534.

I have been working on the idle and I have it doing pretty good but I have run into a situation where I start it up idle is fine, put it in gear and the idle is fine as well. As soon as I put it in park the RPMs run up to 1000 and then stay there until I blip the throttle. I have been staring at this for almost two days but I can figure it out.

Any thoughts? I suspect it is simple but the solution seems to escape me at the moment.

Here is the important data from a export of the bin from TunerPro. Any assistance is greatly appreciated.

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TunerPro Bin Data Export
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Source File: 383-62g.bin

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Constants
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IAC steps fuel addr (msec) 32.77
Closed Loop Timer Warm Thres 60.00 Deg C
Closed Loop Timer Warm Sec's 10.00 Seconds
Closed Loop Timer Cold Sec's 55.00 Seconds
Min Coolant Temp for Closed Loop 58.52 Deg C
Open Loop Idle Thres MPH 2.00 at
Open Loop Idle Thres TPS% 3.91 TPS
Open Loop Idle Off--RPM 600.00
Open Loop Idle On--RPM 1000.00
O/L Idle AFR Enable Time Delay 2.00
O/L Idle AFR Time Delay 2.00
Max O/L AFR at Idle 14.20
O/L Max AFR 14.00
Min O/L AFR at Idle 15.00
Stoich AFR 12.50
Temp thres for Cold Start 11.70 Deg *C
Choke AFR Timeout 1.80 Sec
Choke Hot Timeout 2.00 Sec
Choke Cold Timeout 2.00 Sec
Choke Coolant Hot/Cold Thres 64.00 Deg C
Shutdown Temp 111.00 Deg C
Shutdown Restart Temp 90.00 Deg C
AFR Rich Bias for Hot Restart (subtracted = richer) 0.30
IAC Bias for Hot Restart 40.00
Time for Hot Restart Enable 10.00 Sec
Init for A/C on Steps 25.00
IAC Park Position 50.00
IAC-Park to Run Delay Sec's 40.00
IAC-Stall Saver RPM 500.00
IAC-Exit Stall Saver RPM 525.00
IAC-%TPS for Closed Throttle 2.34
IAC-Delay small error IAC retract 2.00
IAC-Delay large error IAC retract 1.00
IAC-Delay small error IAC extend 1.00
IAC-Delay large error IAC extend 2.00
IAC-RPM enable large error retract 25.00
IAC-RPM enable large error extend 25.00
IAC-Idle Error Tolerance (RPM) 62.50
IAC-DFCO IAC Steps added 40.00
IAC Kickdown Delay Timer 1.00
IAC Kickdown Steps 19.00
IAC steps subtracted Pk to Run 1.00
Max Retract IAC steps 145.00
Max Cold RPM in Kickdown Mode 1200.00 RPM
Max RPM hot Pk/N 1100.00
RPM Added for A/C On 25.00 RPM
Low VSS filter Coef 51.00
Medium VSS filter Coef 51.00
High VSS filter Coef 16.00
IAC extend delay Low VSS (msec) 400.00
IAC extend delay High VSS (msec) 1000.00
IAC Decay Coef (No DFCO) 51.00
DFCO IAC Decay Coef 30.00
Stall Saver IAC step decay coef 38.00
Low VSS thres 3.75 MPH
High VSS thres 20.00 MPH
Min IAC throttle follower steps (Hi VSS) 10.00
Min TPS% for throttle follower 6.00
IAC-Throttle Follower Park/Neutral 12.50 %
IAC-Throttle Follower in Drive 42.97 %
IAC-Max Throttle Follower Bias 30.00 Steps
IAC-Temp for Cold RPM Limiting 0.58 Deg C
IAC-Retract Steps for Voltage Drop 5.00 Retract Steps
IAC-Voltage drop Required 2.00

IAC Position vs Temp

TempC

Cold 81.00
-9 81.00
6 76.00
16 69.00
24 66.00
31 61.00
37 58.00
43 52.00
49 46.00
56 36.00
63 27.00
71 24.00
80 20.00
91 20.00
107 20.00
136 20.00
Hot 20.00


IAC vs. Baro at Reset

kPa

105 20.00
95 20.00
85 25.00
75 30.00
Desired C/L Idle Speed

TempC RPM

115 850.00
110 775.00
105 775.00
100 775.00
95 775.00
85 775.00
75 775.00
65 850.00
55 950.00

 

ttt

No takers?

 

I've fixed this at least once before but I can't remember how and now I wish I had put this in my notebook, lol.
BTW, I can't help you if you don't help me by telling me what ecm/mask you're using. You say 84 vette but have you upgraded to the 7747 or a newer pcm?
What would also help is a complete datalog with flags. The RPM jump might jump high enough to kick it out of idle mode. When this happens the ecm uses a different open loop AFR value based on MAP and not just "idle". From there the SA also changes since when in idle most ecm's have the ability to move the SA up and down to get a desired idle speed. They also use the IAC but combine them all and it's hard to say what is causing your high idle.

 

Ooppss.... Yep it is the 7747 - Prominator Pro. The mask is $42.

Here is the current bin.
Current 7747 Bin

I will capture a datalog with WinAldl tomorrow. Thanks for the assistance.

 

el,

Your IAC vs Temp has a IAC setting of 20 but your Kickdown IAC setting is at 19. It'll never drop. Set the IAC v Temp at 18 or less for the typical operating temps your motor will be at.

 

I already did and it helped a little. I read conflicting posts regarding 1 above or 1 below the iac v coolant. Which is it?

 

Its below. Read RBob's article on IAC control. Otherwise sounds like a sticking throttle. BTW, did you re-set your Min Air?

 

what does 'stoich afr 12.50' mean? {15th line}

statement of fact?
'desired situation'?

related to Arizona fuel or altitude?

 

Check to see that your min TPS for idle isn't set too low and/or your TPS voltage is below .6volts.
Other than that I'd check for the sticking throttle. Have a friend look at the throttle and see if it moves. I also think if you're pretty lean and running a bunch of fuel you can get it to stick high until you flick the throttle. It doesn't happen often but looking at your AFR values I'd say it could be a possibility that your idle AFR is on the lean side. Try zeroing out all of the SA desired idle speed tables and focus on getting your desired idle with the throttle fully closed and using the main SA table.

 

WOW it has been a while. Busy doing things other than the important stuff. Like tuning the Vette....

I have checked the throttle bodies and they are not sticking and they have been set for min air. I have been tuning other parameters and I have my blms in the 123 to 128 range. The issue with the idle jumping to 900rpm from going from drive to park is still there. I have been reviewing the 42 Hack.pdf file and I have learned a bunch but not enough to solve my problem. Keep in mind that I do not touch the throttle. At idle my IAC counts are about 30 and once I put it into drive they go up and then if I go back to park the IAC counts get locked at 50 and stay there until restart. Even blipping the throttle does not help.

I will get it figured out but the interrupt driven code of the 7747 can make your head spin so I have just been taking it once piece at a time. If it was written in C and if I had the source for that I would be alot better off. But it is what it is.

If anyone has any inspiration I am all ears........

 

is it usual and customary to use IAC steps when closed loop at idle? that is for an engine that has bored TB's and possibly a larger cam than stock and runs CL at idle? i have a manual trans (4+3) and took out the IAC steps to "zero" at idle. my TPS is non adjustable and have it at .52 V for TPS. so all the incoming air is from the flow past the butterflies(2.00 inch). my idle is commanded at 750 and in reality it runs 650-850 with a surge. that surge will be worked on when i find time. when air conditioning is turned on my idle moves to 900-950 and is more stable. i may have overcompensated in my tunercat for that AC increased idle but i like it higher.

 

Ron,

The point of lower IAC counts is to bring more air thru the butterflies. IAC counts were used to increase air flow when the venturi diameter couldn't be increased. The more air through the butterflies the faster the air speed which helps to shear and atomize the fuel sprayed in the TB. Helps with low end torque also.

 

Dom - If I am reading this properly then I should strive for the lowest IAC counts possible. Theoretically close to 0 would be best. I set min air once again just to make sure and I also checked my TPS voltage. I am using a feeler gauge because the 2 inch TBs are real sensative and it is hard to get 6 inches of water on the manometer. I am using a 0.002 inch feeler gauge perhaps I shoudl go a little higher with a 383. This would also explain why the 454 bins have a iac at coolant temp at 10 and a kickdown at 9.

 

el,

I think Grumpy would tell you he would run idle with the IACs at close to 0. Again, the higher IAC counts were there when there wasn't an alternative to getting more air through the TBs.
With the larger butterflies now available, you want to keep as much air velocity going through the venturi for better fuel atomization. I see you're using the 2.0 TBs on a 383. I have the 2.13s and have had good luck with them on my 350. Ben is trying out 2.2s on his 383 and I'd say you would probably need more flow as well.
If you bored out the TB's, I'm not sure how you are using a manometer with the throttle plate slit being eliminated. I drilled a hole connecting the center port to the TB base port. I set it using a vacuum gauge and try to get as steady a vacuum as possible paying particular attention when the motor is hot and the cooling fan is running.
Are you using a Xfire or an Xram manifold?
BTW, wouldn't you want your idle IAC count to be below your kickdown? Otherwise the idle will never drop.

 

I am presently using the XRam. I have tried one above and one below the iac vs coolant.

Interesting on the velocity...... hmmmmmm.

 

yes i was aware of the ADV of a IAC at 0 for atomization. here is that word again-atomization. another plus may be the idle speed will be less affected if being manually set to 750 rpms with stop screw at .52 volts yet commanded to 700rpms. anyway helped for me. seems my IAC is awfully happy in that it like to chase its tail inconsistently but that may be cam or BPW related. it clearly is still functioning as it works remarkably well with the air conditioning on.

 

Dom - I tried adjusting the part TF and drive TF but without success. I tried 0 and 100% for both with various combinations in between and disconnecting the battery to remove any values that may be in nvram.

I am at the point of setting the idle manually and adjusting the IAC counts so they are 0. The only IAC parameter I would leave intact would be for the AC - but that may be disabled as well.

FWIW - I have looked at the assy code and I somewhat understand what the IACs are doing but the point still remains after I go from drive to park she idles up. Its got me stumped, that is for sure. The sad thing it is probably something real basic and dumb that I forgot to do.

 

el,

I noticed that your Max RPM PK/N (0x005E2) is set for 900rpm in the bin you sent me. When you do the min air idle adjustment, do you set the rear TB throttle stop so that the rpms are a bit lower than the desired idle rpm? If you have been setting the min air using a feeler gauge, the butterflies may be open too far to allow the idle to drop when in neutral. It drops in D because of the load on the motor.

 

I set the idle with the iac's unplugged and seated and the air hole plugged to 500 rpm. I have tried to go lower but the motor just bucks and snorts.....

Here is the scenario.... I start her up and when she is up to temp she idles at 750, I put her in drive and still at 750 then I put her in to park and the idle goes up to 900.

I am going to try dropping the Max rpm pk/n to 750 and see what happens.

 

That's why I suggested it.

 

No change.... I am going to reset the min air and make it a little tighter with the feeler gauge.

Thanks for the suggestions.